This invention relates to polydiorganosiloxane polyurea segmented copolymers and a process for making the same.
Pressure-sensitive adhesive tapes have been used for more than half a century for a variety of marking, holding, protecting, sealing and masking purposes. Pressure-sensitive adhesive tapes comprise a backing, or substrate, and a pressure-sensitive adhesive. Pressure-sensitive adhesives are materials which adhere with no more than applied finger pressure and are aggressively and permanently tacky. Pressure-sensitive adhesives require no activation, exert a strong holding force and tend to be removable from a smooth surface without leaving a residue. In some applications, interesting pressure-sensitive adhesives are silicone based adhesives.
Traditionally, polydiorganosiloxane pressure-sensitive adhesives have been made in solution. Conventional solvent based polydiorganosiloxane pressure-sensitive adhesives are generally blends of high molecular weight silanol functional polydiorganosiloxanes, i.e., polydiorganosiloxane gums, and copolymeric silanol functional silicate resin, i.e., MQ resins, which comprise R3SiO1/2 units and SiO4/2 units. In order to obtain the desired adhesive properties, it has been necessary to react the copolymeric silicate resin with the polydiorganosiloxane. Improvements in such pressure-sensitive adhesive properties are achieved when the copolymeric polydiorganosiloxane resin and polydiorganosiloxane are intercondensed, providing intra- and inter-condensation within the adhesive. This condensation step requires 1) the addition of a catalyst, 2) reacting the copolymeric polydiorganosiloxane resin and polydiorganosiloxane in solution, and 3) allowing the reaction to take place over a period of time at elevated temperature
Solutions of intercondensed polydiorganosiloxane pressure-sensitive adhesives, are generally applied to a backing, heated to remove solvent, and crosslinked, if necessary, to improve physical properties. If crosslinking is needed, peroxide catalysts are conmnonly used. Disadvantages of solution applied polydiorganosiloxane pressure-sensitive adhesives include the need for elaborate drying ovens to remove solvent, and if crosslinking is required, ovens which operate at temperatures greater than 140xc2x0 C. are needed to initiate diaryl peroxide crosslinking catalysts. Such high oven temperatures limit the substrates useful in making pressure-sensitive adhesive tapes to those which can withstand the elevated temperatures.
In the medical field, pressure-sensitive adhesive tapes are used for many different applications in the hospital and health areas, but basically they perform one of two functions. They are used to restrict movement, such as in various strapping applications, or they are used to hold something in place, such as a wound dressing. It is important in each function that the pressure-sensitive adhesive tape be compliant with and non-irritating to the skin and adhere well to the skin without causing skin damage on removal.
In recent years, pressure-sensitive adhesives have been used in transdermal patch aplications as drug transport membranes or to attach drug transport membranes to skin. Although there is continued development of new drugs and the need for different transport rates of existing drugs, pressure-sensitive adhesives are still needed that can transport such drugs at various rates. Furthermore, there is a continuing need to adhere new drug transport membrances to skin during a treatment period.
In the automotive industry, there are applications that remain unaddressed by current tape products. One such application relates to automative paints and finishes that are formulated for environmental conservation, recyclability, enhanced appearance, improved durability, as well as resistance to environmental sources of contamination. Painted substrates using these new formulations are difficult to adhere to with current tape products. Another application involves mounting thermoplastic polyolefin automotive body side moldings.
Similarly, early electrical tapes were black friction tapes, and the adhesive was soft and often split when unwound. Current electrical tapes have a layer of a pressure-sensitive adhesive applied to a plasticized polyvinyl chloride backing or a polyethylene or rubber film backing. Electrical tape is used to insulate, hold, reinforce and protect electrical wires. Other uses include providing a matrix for varnish impregnation, identifying wires in electrical circuitry, and protecting terminals during manufacture of electrical circuit boards. Electrical tape, should be stretchable, conformable and meet nonflammability requirements.
Corrosion protection materials must be delivered in a conformable form for optimal performance. The ability of pressure-sensitive adhesives to instantly attach to exposed surfaces is very useful for applying protective constructions and for convenient repair of breached protective coatings associated with steel pipelines and related structures subject to corrosion. In these and related applications, the material must not readily flow or be easily rubbed off. Some of the properties of commercially available silicones are known to provide some degree of corrosion protection.
For many heat shrink applications, a single article capable of withstanding high temperature while providing an environmental seal is desired. It is preferable that the adhesive be transparent, to allow viewing of the spliced or protected region. Dual wall heat shrink tubes generally are coextruded tubes of polyolefin (the shrinkable sleeve) and EVA (for hot melt sealing). Use of these products is limited by the rheology of the hot melt. High temperature heat shrink tubes are generally made of fluorinated materials. Hotmelts used in dual wall heat shrink can be of a wide range of materials, as described in U.S. Pat. No. 4,509,820. However, no hotmelt adhesive with satisfactory flow and temperature stability has been identified for use at the shrink temperature of high temperature tubing.
Preformed pavement marking materials include pavement marking sheet materials and raised pavement markers that are used as highway and pedestrian crosswalk markings. They are often reflective and strategically oriented to enhance reflective efficiency when illuminated by vehicle headlamps at night. The marking materials must adhere to a variety of surfaces such as concrete or asphalt, that may be cold, hot, oily, damp, rough or smooth. Present pavement marking adhesive generally have inadequate initial bonding or inadequate permanent bonding to roadway surfaces that are illustrated by five problem areas: (1) limited adhesive tack at cold temperatures resulting in a narrow application window, (2) reduced durability under shear or impact causing difficult removal of temporary markings, (3) low molecular weight fractions in the adhesives on removable markings that stain light colored concrete surfaces, (4) limited ductility allowing raised markers to sometimes shatter upon impact by vehicle tires and (5) insufficient elasticity to fill in gaps between markers and rough road surfaces, thus often leading to premature detachment of the marker from the roadway surface.
Hot melt adhesives are compositions that can be used to bond nonadhereing surfaces together into a composite. During application to a substrate, hot melt adhesives should be sufficiently fluid to wet the surface completely and leave no voids, even if the surface is rough. Consequently, the adhesive must be low in viscosity at the time of application. However, the bonding adhesive generally sets into a solid to develop sufficient cohesive strength to remain adhered to the substrate under stressful conditions.
For hot melt adhesives, the transition from fluid to solid may be accomplished in several ways. First, the hot melt adhesive may be thermoplastic that softens and melts when heated and becomes hard again when cooled. Such heating results in sufficiently high fluidity to achieve successful wetting. Alternatively, the hot melt adhesive may be dissolved in a solvent or carrier that lowers the viscosity of the adhesive sufficiently to permit satisfactory wetting and raised the adhesive viscosity when the solvent or carrier is removed. Such an adhesive can be heat activated, if necessary.
Damping is the dissipation of mechanical energy as heat by a material in contact with the source of that energy. The temperature range and frequency range over which damping occurs can be quite broad, depending upon the particular application. For instance, for damping in tall buildings that experience wind sway or seismic vibrations, the frequency range can go to as low as about 0.1 Hertz (Hz) up to about 10 Hz. Higher frequency damping applications can be those such as for computer disk drives (on the order of 1000 Hz) or higher frequency applications (10,000 Hz). Furthermore, outdoor damping applications expose damping treatments to a wide range of temperature and humidity conditions.
While the performance of a surface layer damping treatment depends largely on the dynamic properties of the viscoelastic material, it is also dependent on other parameters. The geometry, stiffness, mass, and mode shape of the combination of the damping material and the structure to which it is applied will affect the performance of the damping material.
Presently known viscoelastic materials consist of single components or polymer blends. Since presently known single component viscoelastic materials perform over fairly narrow temperature ranges, conventional solutions to wide temperature variations incorporate multiple layers of viscoelastic material, with each layer being optimized for a different temperature range.
The present invention provides compositions comprising (a) polydiorganosiloxane polyurea segmented copolymer compositions comprising the reaction product of (i) at least one polyamine, wherein the polyamine comprises at least one polydiorganosiloxane diamine, or a mixture of at least one polydiorganosiloxane diamine and at least one organic amine, and (ii) at least one polyisocyanate, wherein the mol ratio of isocyanate to amine is between 0.9:1 and 0.95:1 and between 1.05:1 and about 1.3:1, and (b) silicate resins. The composition may optionally contain the product of the addition reaction of at least one polydiorganosiloxane monoamine and at least one polyisocyanate and optionally polydiorganosiloxane diamine. The composition may also optionally contain nonreactive additives such as fillers, pigments, stabilizers, plasticizers, organic tackifiers, antioxidants, compatibilizers and the like. The composition may also have vibration damping, PSA, hot melt, and corrosion protection characteristics.
The present invention further provides a tackified polydiorganosiloxane polyurea segmented copolymer composition comprising (a) a polydiorganosiloxane polyurea segmented copolymer with alternating soft polydiorganosiloxane units and hard polyisocyanate residue units, (wherein the polyisocyanate residue is the polyisocyanate minus the xe2x80x94NCO groups), and optionally, soft and/or hard organic polyamine units, and such that the residues of the amine and isocyanate units are connected together by urea linkages. Compositions of the present invention typically have inherent viscosities of at least 0.8 dL/g, or are essentially insoluble in common organic solvents such as, for example, chloroform, tetrahydrofuran, dimethyl formamide, toluene, isopropyl alcohol, and combinations thereof, and (b) silicate resin. The composition may optionally contain the product of the addition reaction of at least one polydiorganosiloxane monoamine and at least one polyisocyanate and optionally polydiorganosiloxane diamine. The composition may also have vibration damping, PSA, hot melt, and corrosion protection characteristics.
The compositions of the present invention are particularly useful as pressure-sensitive adhesives and in one aspect of the present invention, the pressure-sensitive adhesives (PSAs) can be used to fabricate PSA articles, wherein the PSA articles comprise a flexible substrate and a layer of PSA prepared according to the present invention. Furthermore, the substrate may be any substrate that would be known to those skilled in the art, may be previously made or coextruded with the PSA, and may further be coated or treated to provide a low energy release surface, such as coating with a low adhesion backsize, a release coating and the like. In addition, the substrate may be made of a low surface energy material such as, for example, TEFLON(trademark) and polyolefins. Particularly useful articles include medical tapes, transdermal drug delivery systems, corrosion protection tapes and pavement markers.
In another aspect of the present invention, hot melt adhesives can be used as prepared rods, sheets, pellets and the like that can be subsequently applied in a molten state or heat activated to produce an adhesive bond between different substrates. The substrate may be any substrate that would be known to those skilled in the art and the invention would be especially useful in adhering low surface energy materials and electronic components.
The polydiorganosiloxane polyurea segmented copolymer pressure-sensitive adhesives in this invention provide to metal substrates superior corrosion protection and ease of application. They also offer the appropriate combination of viscosity, thermal stability and transparency for heat shrink applications.
The present invention also provides a vibration damping composite comprising at least one substrate and at least one layer of the composition of the present invention The substrate may be flexible, stiff, or rigid. Furthermore, the substrate may be any substrate that would be known to those skilled in the art and may further be coated or treated to provide a low energy release surface, such as coating with a low adhesion backsize, a release coating and the like.
Such composites may be a constrained layer construction, wherein the construction comprises at least one substrate having a stiffness sufficient to cause resonation within the substrate in response to an internal or external applied force and at least one layer of the composition of the present invention. The constrained layer construction preferably has a composite loss factor, tan 5 greater than or equal to 0.40 in the temperature range of between about xe2x88x9280 and 150xc2x0 C. and in the frequency range of 0.01 to 100,000 Hz as evaluated by a Polymer Laboratories Dynamic Mechanical Thermal Analyzer Mark II in the shear mode. The useful temperature range depends on both the frequency and the characteristics of the damping composition.
In another aspect, the composite article construction may be such to provide a bidirectional vibration damping constrained layer construction comprising at least two rigid members, and at least one layer of the composition of the present invention. Generally, each rigid member has a stiffness exceeding that of a 0.25 cm steel plate. Preferably, the vibration damping composition has a tan xcex4 greater than or equal to 0.4 in the temperature range of xe2x88x9280xc2x0 C. and 150xc2x0 C. and in the frequency range of 0.1 to 10 Hz, as evaluated by a Polymer Laboratories Dynamic Mechanical Thermal Analyzer Mark II in the shear mode.
Advantageously, shaped articles can be produced, for example, by techniques such as compression molding, injection molding, casting, calendaring and extrusion.
The compositions of the present invention have excellent physical properties typically associated with polydiorganosiloxane polymers such as moderate thermal and oxidative stabilities, UV resistance, low surface energy and hydrophobicity, resistance to degradation from exposure to heat and water, good dielectric properties, good adhesion to low surface energy substrates, low index of refraction, and flexibility at low temperatures. In addition, the compositions exhibit a combination of unexpected properties including, for example, excellent mechanical strength upon cooling, allowing subsequent operations to contact the surface soon after the compositions have been applied, excellent damping performance over a broad temperature range, an ability to withstand large strains, excellent adhesion to a variety of substrates when formulated for adhesion, and handling characteristics that permit easy attainment of desired thicknesses and shapes.
The compositions of the invention have good resistance to environmental conditions and good performance over a broad range of frequency and temperature. Vibration damping compositions of the present invention have wide utility for minimizing adverse vibration in constrained layer damping treatments as well as minimizing adverse wind sway and seismic influences in buildings subject to wide temperature and humidity variations.
The polyurea functionality of the polydiorganosiloxane-based compositions allows the formulation to take advantage of thermally disassociable crosslinks that are formed via hydrogen bonding of the urea functional groups in the polymer backbone. These crosslinks are thermally disassociated during hot melt processing to allow coating and can reform on cooling to restore the original mechanical properties without the need for additional crosslinking agents.
The present invention further provides a method of making a melt processable composition comprising the steps of mixing a polyamine with a polyisocyanate in a heated vessel, reacting the two to make polydiorganosiloxane urea segmented copolymer and adding a silicate tackifying resin. The process is preferably carried out under substantially solventless conditions. The silicate tackifying resin can be added at any point in the process, preferably before or during the reaction step, and more preferably before the reaction step. Optionally the silicate tackifying resin can be subsequently added to the reacted polydiorganosiloxane polyurea segmented copolymer in solution.
The substantial elimination of solvent in the process of the present invention has many advantages involving the environment, economics, and safety. This solventless process is environmentally advantageous as there are no solvents to be evaporated from the final composition. The continuous nature of this process has several other inherent advantages over conventional solution polymerization processes. The isocyanate to amine ratio can be varied below and, more notably, above 1:1 to optimize the properties while still obtaining strong, extrudable materials. Another advantage of this process is the ability to utilize high molecular weight polydiorganosiloxane polyurea segmented copolymers which are not obtainable using solution polymerization processes due to the insolubility of the forming polymer in the solvent medium or excessively high viscosities at practical solution concentrations.
Yet another advantage of this substantially solventless, continuous process is the ability to add or blend, in line, the silicate resin, as well as various fillers, and other property modifiers into the polydiorganosiloxane polyurea segmented copolymer before, during, or after formation of the copolymer.
Optionally, nonreactive additives such as fillers, plasticizers, pigments, stabilizers, antioxidants, flame retardants, compatibilizers and the like may be added at any point in each of the above processes.